Exposure method and exposure system the same

ABSTRACT

In lithographic (exposure) processing for semiconductor device fabrication, the task of extracting exposure parameters is performed by calculating exposure energy and focus offset using a test wafer for each exposure device, because fluctuations due to differences between exposure devices are large. For the fabrication of semiconductor devices in multiple-product small-lot production, the number of times the task of extracting exposure parameters has to be performed increases, so that the operation ratio of the exposure devices decreases, and the TAT of the semiconductor device fabrication increases. Moreover, as the miniaturization of semiconductor devices advances, differences between the exposure devices cause defects due to the exposure processing, and the yield of the semiconductor device fabrication decreases. In an improved method of exposure processing for semiconductor devices, the exposure energy and focus offset according to the illumination parameters for an exposure device and optical projection system, using information regarding the projection lens aberrations of a plurality of exposure devices, the photoresist parameters, and the circuit pattern information, as determined beforehand, are calculated using an optical development simulator, and the exposure processing is carried out using an exposure device, selected from a plurality of exposure devices, in which the process window is within a certain tolerance value.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent ApplicationNo. 2000-391824, filed Dec. 20, 2000.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

[0002] NOT APPLICABLE

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK.

[0003] NOT APPLICABLE

BACKGROUND OF THE INVENTION

[0004] 1. Field of the Invention

[0005] The present invention relates to a method for fabricatingsemiconductor devices, and more particularly to a method forlithographic processing, in which a circuit pattern is transferred ontoa semiconductor device.

[0006] 2. Description of the Related Art

[0007] When, in the fabrication of semiconductor devices, a circuitpattern is lithographically transferred to a substrate wafer of asemiconductor device (hereinafter referred to as “wafer”), numerousexposure steps and etching steps are necessary. FIG. 2 illustrates amethod for transferring a circuit pattern onto an insulating film formedon the wafer. First, in an exposure step, a circuit pattern istransferred onto a photoresist film on the wafer. Then, in an etchingstep, using the photoresist pattern formed in the exposure step as amask, a circuit pattern is formed in the insulating film on the wafer.More specifically, in a first exposure process a photoresist film isformed on the wafer by an application process. In a second exposureprocess, the circuit pattern is transferred to the photoresist using anexposure device. After that, the exposed photoresist is put through adeveloping process to form a photoresist pattern.

[0008]FIG. 3 shows the configuration of a reduction projection exposuredevice used mainly for the lithographic (hereinafter “exposure”) step.With this exposure device, a circuit pattern formed by etching metal ona glass “reticle” (a mask usually made of quartz glass) is exposedthrough a reduction lens, to pattern one or more chips on a wafer at atime. By changing the reticles in subsequent exposure steps, the circuitpatterns necessary for fabricating a semiconductor device can be formedon the wafer. With the resolution of the circuit pattern and the patternarrangement that takes place in the exposure steps, it is possible tooptimize the illumination conditions of the optical projection system ofthe exposure device, such as the numerical aperture NA and theillumination coherency σ, as well as the photoresist parameters (type,thickness, etc.).

[0009] In order to satisfy the electrical properties of a semiconductordevice, not only the resolution, but also the variations in thedimensions of the transfer pattern have to be within tolerance ranges.For example, variations in the gate dimension of a transistor may causevariations in the threshold voltage of a transistor, so that variationsin the photoresist pattern dimensions have to be set within a certaintolerance range. There are many causes of dimensional fluctuations inthe photoresist pattern, such as focus shifts, discrepancies whenproducing the circuit pattern on the reticles, aberrations in thereduction lens of the exposure device, or variations caused by theapplication or developing processes. In actuality, the fluctuations inthe exposure device are the most important, so that the exposure energyand the offset of the focus when transferring a circuit pattern are setfor each reticle, exposure step, and exposure device, and the dimensionof the photoresist pattern portion with the smallest margin in theexposure steps (critical dimension, hereinafter referred to as “CD”) isadjusted to be within a certain tolerance value. At present, the optimumvalues for the exposure energy and the focus offset are calculated foreach reticle, exposure step and exposure device by measuring the CD of atest wafer that is exposed with different exposure energies and focuses(also called “extracting the exposure conditions”). At this time, aprocess window of exposure energy and focus, in which the CD values arewithin a certain tolerance value, is produced, and the central value ofthat window is taken as the optimum value of exposure energy and focusoffset. Moreover, the larger the window, the higher is the margin withrespect to CD fluctuations in the exposure step, so that the processwindow can be used as an assessment index of the exposure step. FIG. 4illustrates a method for calculating the optimum values of exposureenergy and focus offset using the process window for the exposure step.The process window of the exposure energy and focus is calculated usingthe CD values of a test wafer that is exposure processed while changingthe exposure energy and the focus offset within a certain tolerance.Here, an example is shown in which, for the same reticle, the processwindows as well as the final optimum exposure energy and focus offsetdiffer depending on whether device A or device B is used for theexposure step.

[0010] On the other hand, fabrication for multiple-product small-lotproduction of semiconductor devices increases the number of times theexposure parameters must be extracted, a task which is performed foreach reticle, exposure step and exposure device, so that the TAT(turn-around time) for newly ordered/in-process semiconductor devices inincreases as well. It is possible to limit the number of times the taskof extracting the exposure parameters is performed by fixing theexposure parameters of the exposure devices used for each type ofsemiconductor device, but variations in the operation ratio of exposuredevices occur, which lead to a lower throughput of all exposure steps.

[0011] As a way to solve this problem, Aida et al. (ElectronicInformation Society, Introduction into Response Surface Functions ForStatistical Design of Optical Lithography Processes, 1996), for example,have proposed a method for producing response surface functions of CDvalues, using exposure energy, focus offset and the illuminationparameters of the optical projection system (numerical aperture NA andillumination coherency σ) as variables, and calculating exposure energyand focus offset from these response surface functions.

[0012] To increase the operation ratio of the fabrication equipment, asystem for automatically selecting and assigning equipment in accordancewith the operation ratio of the fabrication equipment, also referred toas “dispatching”, which depends on certain rules such as “FIFO” or“priority on delivery time”, has been implemented (for example,“Siview”, IBM Japan), and is currently used for the assignment ofexposure devices.

[0013] Furthermore, JP H11-267952A proposes a production control system,in which the fabrication variations in each step are reduced and thequality and yield are improved.

[0014] In the fabrication of multiple-product small-lot production ofsemiconductor devices such as system LSIs, the number of times the taskof extracting the exposure parameters is performed for each reticle,exposure step and exposure device for the fabrication of new products,and the TAT of the products are higher than for mass-produced productssuch as memory devices. By fixing the exposure parameters of theexposure devices used for each type of semiconductor device, the numberof times the task of extracting the exposure parameters has to beperformed can be reduced, but this causes irregularities in theoperation ratio, and leads to a decrease in the throughput of allexposure steps.

[0015] In the approach for calculating the exposure energy and focusoffset proposed by Aida et al., as mentioned above, it is possible tocalculate the optimum values of exposure energy and focus offset due todifferences in the illumination parameters of the optical projectionsystem. However, to calculate the exposure energy and focus offset for aplurality of exposure devices is problematic: there are differencesbetween the exposure devices, such as differences in the aberrations ofthe projection lenses, so that the response surface functions have to beproduced and corrected for each exposure device. Furthermore,information regarding the circuit pattern is not taken into account, sothat it is not possible to correct fluctuations of the exposure energyand the focus offset that depend on the circuit pattern.

[0016] In dispatch systems that have been put into practice, the devicesthat are used can be assigned based on the operation conditions andin-process information of the current fabrication equipment, but thenumber of times that the task of extracting the exposure conditions hasto be performed cannot be reduced. Accordingly, it is not possible toassign exposure devices for which the setting of the exposure parametershas not been carried out, and such devices cannot be used to diminishthe increase in the TAT of semiconductor devices caused by the increasein the number of times that the task of extracting the exposureconditions has to be performed for multiple-product small-lotproduction.

[0017] In JP H11-267952A, a combination of fabrication devices isselected using workmanship data when machining is performed. Becausethere is no workmanship data in the case of newly ordered/in-processsemiconductor devices, this approach cannot be used in such cases.

[0018] Moreover, if the miniaturization of the device patternprogresses, even with the same illumination conditions, the processwindows will fluctuate depending on differences among the exposuredevices due to the aberrations of their projection lenses, so that theproduction yields for the semiconductor devices will also vary due tothe differences among the exposure devices. When forming very detailedcircuit patterns, it is necessary to perform exposure processing aftercomparing the process windows of a plurality of exposure devices, andselecting an exposure device with a large process window, to improve theyield.

SUMMARY OF THE INVENTION

[0019] It is thus an object of the present invention to present a methodfor lithographic processing of semiconductor devices and an exposuresystem for use in that process that has a means for calculating themargins of exposure energy and focus, as well as for calculating theoptimum values of exposure energy and focus offset, which changedepending on the aberration of the projection lenses of the exposuredevices; and a means for assigning an exposure device used for suchprocessing, based on the calculated margins of exposure energy andfocus.

[0020] The present invention includes, in one embodiment, a firstdatabase storing aberration information (for example, Zernikecoefficients) of projection lenses of a plurality of exposure devices; asecond database storing process specification information such asillumination parameters (e.g., exposure wavelength, numerical apertureNA of lenses, illumination coherency σ); photoresist parameters (e.g.,type, thickness and development time) and tolerance CD values for theexposure steps of the semiconductor device fabrication; a third databasestoring circuit pattern information used for the exposure steps of thesemiconductor device fabrication; a fourth database storing dispatchrules of the exposure devices; a fifth database in which the margins ofexposure energy and focus as well as the optimum values of exposureenergy and focus offset for the steps on the plurality of exposuredevices are registered; an exposure parameter calculation processingportion for calculating the margins of exposure energy and focus as wellas the optimum values of exposure energy and focus offset; and anexposure device assignment processing portion for selecting an exposuredevice to be used for the exposure step based on the margins of exposureenergy and focus of the plurality of exposure devices and the dispatchrules of the exposure device, and executing the exposure processing.

[0021] The exposure parameter calculation processing portion performs:

[0022] (1) a step of looking up illumination parameters of the opticalprojection system used for the exposure processing and photoresistparameters;

[0023] (2) a step of looking up circuit pattern information used for theexposure processing;

[0024] (3) a step of looking up aberration information of the projectionlens of the exposure device; and

[0025] (4) a step of calculating margins of exposure energy and focus aswell as optimum values of exposure energy and focus offset for exposureprocessing with an optical development simulator, based on theinformation looked up in steps (1) to (3).

[0026] By executing steps (1) to (4) in order, it becomes possible tocalculate exposure energy and focus offset in consideration of thefluctuations of the process windows due to aberrations of the projectionlenses of the exposure devices without performing the task of extractingthe exposure parameters.

[0027] The exposure device assignment processing portion performs:

[0028] (5) a step of looking up the margins of exposure energy and focusfor a plurality of exposure devices calculated by the exposure parametercalculation processing portion;

[0029] (6) a step of looking up the dispatch rules of the exposuredevices; and

[0030] (7) a step of selecting an exposure device based on the marginsof exposure energy and focus as well as the dispatch rules.

[0031] By executing the steps (5) to (7) in order, it becomes possibleto carry out exposure processes with exposure devices having taken intoconsideration the fluctuations of the process windows and the deviceoperation state.

[0032] Thus, the exposure energy and focus offset, which fluctuatedepending on the aberration of the projection lens of the exposuredevice, can be determined without performing the task of extracting theexposure parameters. Furthermore, it becomes possible to improve theproduction yield of the semiconductor devices by selecting, from aplurality of exposure devices, an exposure device with a large processwindow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a block diagram showing a first embodiment of a methodused during a lithography process for exposing semiconductor devices inaccordance with the present invention and a system therefor;

[0034]FIG. 2 is a diagram illustrating a pattern transfer method for thefabrication of semiconductor devices;

[0035]FIG. 3 is a diagram showing the configuration of a reductionexposure projection device;

[0036]FIG. 4 is a diagram illustrating a method for calculating exposureenergy and focus offset;

[0037]FIG. 5 is a diagram illustrating the variations of the processwindows due to different aberrations of the projection lenses;

[0038]FIG. 6 is a diagram illustrating a method for calculating theaberrations of the projection lenses;

[0039]FIG. 7 is a flowchart illustrating a method for calculating themargins for exposure energy and focus as well as for calculating theoptimum values of exposure energy and focus offset in accordance withthe present invention;

[0040]FIG. 8 is a flowchart illustrating a method in accordance with thepresent invention for performing exposure processing by selecting anexposure device in which the margins for exposure energy and focus arelarge;

[0041]FIG. 9 is a diagram showing an example of an output screen of thecalculation results for the exposure device, reticle, exposure energyand focus offset in accordance with the present invention;

[0042]FIG. 10 is a block diagram illustrating a second embodiment of thepresent invention;

[0043]FIG. 11 is a block diagram illustrating a third embodiment of thepresent invention; and

[0044]FIG. 12 is a diagram illustrating a method for selecting anexposure device in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0045] The following is a description of the preferred embodiments ofthe present invention, with reference to the accompanying drawings.

[0046]FIG. 1 is a block diagram showing the overall configuration of afirst embodiment of the present invention. In FIG. 1, an exposure devicegroup 1 is configured with at least two exposure devices 2. The exposuredevices 2 are devices having an optical projection system for patterntransfer. The exposure device group 1 is connected to a data computationstation 3 including an exposure parameter (i.e., exposure energy andfocus offset) calculation processing portion 4, an exposure deviceassignment processing portion 5, an input/output interface 6, and adatabase portion 7. Moreover, the exposure device group 1 is connectedto a fabrication control system 10 for controlling the overallsemiconductor device fabrication line. During the exposure processing,the semiconductor device type, process step and wafer name can beentered, for example, by reading a serial number provided on the wafer,and sent over a network from the fabrication control system 10.

[0047] A reticle set 8 that is made of at least two reticles 9 isconnected to the data computation station 3 and the fabrication controlsystem 10. The semiconductor device type for which the reticles are usedand the exposure step can be entered, for example, by reading a serialnumber formed on the reticle, and can be obtained over a network fromthe fabrication control system 10. It is also possible that there are aplurality of reticles for the same semiconductor device type or exposurestep.

[0048] The database portion 7 includes a projection lens aberrationdatabase 71 in which the projection lens aberration information (such asthe Zernike coefficients) for the exposure devices is stored; a processspecification database 72 in which the illumination parameters (such asexposure wavelength, numerical aperture NA of the lens, illuminationcoherency σ) of the optical projection system and the photoresistparameters (such as type, thickness developing time) for the variousexposure steps of the semiconductor device are stored; a reticle circuitpattern database 73 in which reticle circuit pattern information such asthe circuit pattern of the semiconductor device and the measurementresults of fabrication discrepancies of the reticles are stored; adispatch rule database 74 in which dispatch rules for selecting theexposure device used for the exposure processing are registered; and anexposure parameter database 75 in which the exposure parameters (such asexposure energy and focus offset) for each exposure device 2 andsemiconductor device exposure step are registered. In response toqueries from the exposure parameter calculation processing portion 4 andthe exposure device assignment processing portion 5, the relevant dataare looked up over the input/output interface 6 and the data serving asthe query reply are sent to the exposure parameter calculationprocessing portion 4 or the exposure device assignment processingportion 5.

[0049] Based on the data obtained from database portion 7 and using anoptical development simulator, the exposure parameter calculationprocessing portion 4 calculates the margins for exposure energy andfocus as well as the optimum values for exposure energy and focus offsetwhen performing exposure processing with the exposure devices 2. Theresults of that computation are registered via the input/outputinterface 8 in the exposure parameter database 75 of the databaseportion 7. Here “margin” means the range of the exposure energy andfocus offset that is within the specification of the CD, and the unitfor the margin of the exposure energy is quantity of light, whereas theunit for the focus offset is stage driving distance. If the margins areexceeded, the CD leaves the specification, and defects occur in thesemiconductor device. Moreover, the center of the range of exposureenergy is the optimum exposure energy, and the center of the range ofthe focus offset is the optimum focus offset.

[0050] Based on the data obtained from database portion 7, the exposuredevice assignment process portion 5 selects an exposure device and areticle for carrying out exposure processing from exposure device group1 and reticle set 8, and the exposure parameters (exposure energy andfocus offset) are sent over input/output interface 6 to the exposuredevices 2.

[0051] Fabrication control portion 10 supervises the operating conditionof exposure devices 2 in exposure device group 1 and reticles 9 inreticle set 8, as well as the in-process information of the wafer, andsends reply data in response to queries from the exposure deviceassignment processing portion 5.

[0052]FIG. 5 shows the fluctuation of the exposure energy and the focusoffset due to different aberrations of the projection lenses assimulated with an optical development simulator. In the case ofspherical aberration, the optimum value of the focus offset fluctuatesmore than without aberrations. Without aberration, the exposure devicehas to be corrected by an offset of 0.1 μm, and with an aberration of0.05λ, the exposure device has to be corrected by an offset of 0.2 μm.

[0053]FIG. 6 illustrates a method for measuring the aberration of aprojection lens.

[0054] (1) First, an aberration measurement pattern is formed generatingpositional deviations causing an aberration exposed over a focusingmicrolens.

[0055] (2) Then, a reference pattern is formed overlapping theaberration measurement pattern, such that positional deviations causingaberration are not generated.

[0056] (3) Then, the shift between the reference pattern and theaberration measurement pattern depending on the height of the lens imageis measured.

[0057] (4) From the shift between the reference pattern and theaberration measurement pattern in the lens plane, it is possible tocalculate the wavefront aberrations, and from the obtained wavefrontaberrations it is possible to calculate the Zernike coefficients.

[0058] In this embodiment, the Zernike coefficients are stored in thedatabase as the aberration information of the projection lens.

[0059]FIG. 7 is a flowchart illustrating the method for calculating themargins for exposure energy and focus as well as the optimum values ofexposure energy and focus offset. First, in Step 101, the type ofsemiconductor device to be processed and the exposure step are obtainedfrom the fabrication control system. In Step 102, the type ofsemiconductor device as obtained in Step 101, the exposure device usedfor the exposure step, and the reticle information are obtained from thefabrication control system, and a list of exposure devices and reticlesis produced. In Step 103, the exposure device and the reticle with whichprocessing is performed are set as the initial values in the list ofexposure devices and reticles. In Step 104, the illumination parameters,the photoresist parameters and the CD tolerances are looked up in thestep specification database. Then, in Step 105, the circuit patterninformation of the reticle to be processed is looked up. It should benoted that the reticle circuit pattern information includes type ofreticle (usually, phase-shift, Levenson, etc.), pattern dimensions,pattern layout (repeating, isolated), pattern fabrication discrepancies,etc. In Step 106, the aberration functions of the projection lens of theexposure device used for the process are looked up in the projectionlens aberration database. In Step 107, based on the data looked up inSteps 104 to 106, the range of exposure energy and focus that are stillwithin the CD tolerance value is calculated with an exposure/developmentsimulator, and a process window is produced. At this time, using theaberration functions of the projection lens, the wavefront aberration ofthe projection lens is generated with the exposure/developmentsimulator. Then, the circuit pattern form corresponding to the wavefrontaberration of the projection lens for different exposure energies andfocus offsets is generated, and the CD values are calculated.

[0060] In Step 108, after determining the center of the process windowcalculated in Step 107, the optimum exposure energy and focus offset iscalculated, and, by combining information from the exposure parameterdatabase regarding the type of semiconductor device, the exposure step,the exposure device and the reticle, the margins for exposure energy andfocus, as well as the optimum values of exposure energy and focusoffset, are registered. In Step 109, it is determined whether theexposure device used for processing is the last one in the list ofexposure devices. If it is not the last one, then the device is updatedin Step 110, and the process is repeated from Step 106 onward. If theexposure device used for processing is the last one, then it isdetermined in Step 111 whether the reticle to be processed is the lastone. If it is not the last one, then the exposure device is returned tothe initial value, the processed reticle is updated, and the process isrepeated from Step 105 onward. If the reticle is the last one, then theprocess is terminated.

[0061]FIG. 8 is a flowchart showing a method for performing exposureprocessing by selecting an exposure device in which the margins forexposure energy and focus are large. First, in Step 201, the type ofsemiconductor device subjected to the exposure processing and theexposure step are obtained from the fabrication control system. In Step202, the operating information for a plurality of exposure devices isobtained from the fabrication control system. The operating informationfor an exposure device includes the operating conditions of the exposuredevice and the in-process information of the semiconductor device to besubjected to the next process. In Step 203, the type of semiconductordevice to be subjected to processing, as obtained in Step 201, the useconditions of the reticle to be used for the exposure step, and thesubsequent use schedule are obtained from the fabrication controlsystem. In Step 204, the dispatch rules of the semiconductor device tobe subjected to exposure processing are looked up. In the dispatchrules, the priority rules for each semiconductor device applied toproduction progress and the assigning of the equipment in accordancewith ordering conditions and yield conditions of the fabrication processare defined in IF-THEN format, for example. In Step 205, the processwindow the exposure step information for a plurality of exposure devicesis looked up. In Step 206, the exposure device performing the exposureprocessing is calculated based on the dispatch rules obtained in FIG.204. For example, in a semiconductor device for which it has beendefined in the dispatch rules that the yield is important, assignment ismade with regard to a device and a reticle in which the area of theprocess window is equal to or greater than the tolerance value in theexposure step, regardless of the operating conditions of the exposuredevices and the use conditions of the reticles, thus improving theyield. And with dispatch rules considering both production progress andyield, the priority of exposure device and reticle in view of productionprogress and the priority of exposure device and reticle in view ofyield are weighted, and the exposure device and reticle with the highesttotal priority are assigned. In Step 207, the optimum values for theexposure energy and focusing offset are looked up using the combinationof the exposure device and reticle calculated in Step 206. In Step 208,exposure processing is performed using the exposure device, reticle,exposure energy and focus offset calculated in Steps 206 and 207.

[0062]FIG. 12 illustrates a dispatch method that takes intoconsideration both production progress and progress yield fordetermining the optimum exposure device and reticle (Step 206 of FIG.8). In view of production progress, the assessment index P1 of theexposure device to be used is determined with respect to the operatingconditions of the exposure device, the use conditions of the reticle andthe delivery time of the semiconductor device to be processed.

[0063] When the semiconductor device has reached the exposure processingstage, the optimal exposure device to use for the lithographicprocessing of device in question is selected from an exposure devicegroup made up of the plurality of exposure devices used for exposureprocessing of each type of semiconductor device. At this time, in a casewhere priority is given to delivery times, the method for assigning theorder in which semiconductor devices are to be processed compares thenumber of days remaining until the delivery of the devices directlyawaiting assignment with the number of days remaining until delivery ofthe other semiconductor devices waiting for exposure processing, anddecides that the highest priority be given the to semiconductor deviceswith the fewest days left until delivery. Then, in the order of thehighest priority position, the operating conditions of the exposuredevice and the use conditions of the reticle are determined, and if useis possible, then exposure processing is carried out. Moreover, if theexposure device and the reticle cannot be used, then a reservation ismade, and the exposure processing is carried out as soon as use becomespossible. For example, the time required to complete the exposureprocesses for the various exposure devices is added up, and assessmentindex P1 of the semiconductor devices directly awaiting assignment iscalculated from that length of time. For example, if the assessmentindex P1 for the various exposure devices is expressed by numbers from 0to 10, then the exposure devices are arranged in the order of the timerequired for processing completion, and the value obtained by dividingthe priority position by the total number of devices is used. In thatcase, the higher the priority, the larger the index. It is also possibleto determine, individually and in advance, the range oftime-to-completion for each index, and to set the index in accordancewith that range. Here, a method of assigning exposure devices forcarrying out the exposure of the semiconductor devices in accordancewith the delivery times and the use conditions of the exposure devicesand reticles was explained, but the assigning of exposure devices can besimilarly carried out, not only in view of delivery, but also in view ofother aspects, such as the remaining number of steps or whether there isan operation of reproducing the semiconductor devices.

[0064] On the other hand, with regard to yield, the assessment indicesP2 of the exposure devices used are calculated in accordance with thesize of the process window of the exposure devices (margins for exposureenergy and focus offset). The overall assessment indices P arecalculated by weighting assessment index P1 with weighting functionscalculated in view of production progress, and by weighting assessmentindex P2 with weighting functions calculated in view of the yield, asdefined in the dispatch rules, and the exposure device that is actuallyused is the one with the largest assessment index P.

[0065] The following is an explanation of a method for setting theweighting functions. Usually, the scheduled completion time of theexposure steps is specified in advance, based on the delivery time ofthe semiconductor devices awaiting assignment. The assessment indices P1are calculated based on the time-to-completion of the exposureprocesses, so that the margin for the delivery time in the exposure stepfor the next exposure process is determined by calculating thedifference between the two values. If this value is positive, then theexposure process can be finished earlier than planned, and if it isnegative, then the exposure processing will be finished later thanplanned. Moreover, the assessment indices P2 are determined bycalculating the size of the process window, and if the process window issmall, this affects the yield. The relationship between the processwindow and the yield can be determined from the results of evaluatingsamples of past exposure processing of semiconductor devices. At thistime, the obtainable number of chips is separately calculated for eachexposure process completion time for the semiconductor devices awaitingassignment. Assessment index P1 is given greater weight if the number ofobtainable chips of semiconductor devices awaiting assignment is low, asdetermined by subtracting the number of chips already produced from thenumber of chips ordered and comparing that number with the number ofobtainable chips of semiconductor devices awaiting assignment.Conversely, if a maximum number of obtainable chips of semiconductordevices awaiting assignment is needed, then assessment index P2 is givengreater weight. For example, consider assignment when there is asemiconductor device 1 with an assessment index P1 of 1 and anassessment index P2 of 2, and a semiconductor device 2 with anassessment index P1 of 2 and an assessment index P2 of 1. If there isstill time remaining before the delivery time of the semiconductordevice directly awaiting assignment, then the exposure device with thehighest total index P is assigned as the exposure device with which theassigned semiconductor device will be processed, and the exposureprocess is carried out. If the exposure device and the reticle arecurrently being used, then a reservation is made for the exposure deviceand the reticle, and the process is carried out when they are free foruse. Moreover, if the assigned exposure device cannot be used due to adefect or the like, then the exposure device with the next highest totalindex is assigned.

[0066]FIG. 9 is a diagram showing an example of an output screen of thecalculation results for the exposure device, reticle, exposure energyand focus offset in Steps 207 and 208 of FIG. 8. The name of thesemiconductor device, the exposure step, the exposure device performingthe exposure process, the name of the reticle, the exposure energy andthe focus offset are displayed (though not show in the figure). Itshould be noted that the output screen displays on the exposure device,on an output terminal of the fabrication control system or on adedicated output terminal.

[0067]FIG. 10 is a block diagram illustrating a second embodiment of thepresent invention. It should be noted that elements equivalent to thosein FIG. 1 are marked by like numerals. In this embodiment, datacomputation station 3 including database portion 7, exposure parametercalculation processing portion 4, and exposure device assignmentprocessing portion 5, is built into fabrication control system 10, andall processes are performed.

[0068]FIG. 11 is a block diagram illustrating a third embodiment of thepresent invention. It should be noted that elements equivalent to thosein FIG. 1 are marked by like numerals. In this embodiment, datacomputation station 3 including database portion 7, exposure parametercalculation processing portion 4, and exposure device assignmentprocessing portion 5, is built into each of the exposure devices 2, andall processes are performed.

[0069] The above-described embodiments have been explained forapplication of the present invention to exposure devices used in thefabrication of semiconductor devices, but the present invention is notlimited to the fabrication of semiconductor devices, and can similarlybe applied to manufacturing methods using projection-type exposuredevices.

[0070] The present invention calculates the exposure energy and thefocus offset set for each exposure device in the exposure steps ofsemiconductor device fabrication, using previously obtained projectionlens aberrations of the exposure devices in accordance with illuminationparameters of the optical projection system, photoresist parameters, andcircuit pattern information. In addition, the present invention uses anoptical development simulator, to reduce the number of times exposurecondition extraction has to be performed in semiconductor deviceexposure processing where a plurality of exposure devices is used, andthe exposure energy and focus offset must be calculated, using testwafers, for each exposure step and exposure device. Accordingly, theoperation efficiency of the exposure devices can be improved, and theTAT of semiconductor devices can be diminished.

[0071] Moreover, the present invention has the function of carrying outexposure processing with a selected exposure device, from a plurality ofexposure devices, that has a large process window, so that defectscaused by the exposure step in a new semiconductor device fabricationcan be decreased, and the yield can be improved.

What is claimed is:
 1. A method for exposure processing of asemiconductor device in which a predetermined pattern is transferredonto a semiconductor device, comprising: a step of reading, from adatabase, illumination parameters, photoresist parameters, circuitpattern information and aberration information of projection lenses usedin a plurality of exposure devices, for carrying out the patterntransfer; a step of performing optical development simulation based onthe illumination parameters, photoresist parameters, circuit patterninformation and the plurality of sets of aberration information, forcarrying out the pattern transfer; a step of calculating margins ofexposure energy and focus as well as optimum values of exposure energyand focus offset; and a step of carrying out the exposure process using,from the plurality of exposure devices, an exposure device for which themargins of exposure energy and focus satisfy a predetermined tolerance.2. The method for exposure processing of a semiconductor device inaccordance with claim 1, further comprising: a step of calculating anassignment priority order of exposure devices using the margins ofexposure energy and focus in the plurality of exposure devicescalculated by the calculation step; and an exposure device assignmentstep of selecting an exposure device used for the exposure processingbased on the priority order of the exposure devices.
 3. The method forexposure processing of a semiconductor device in accordance with claim1, wherein the exposure parameter calculation step determines, with anoptical development simulator, ranges of exposure energy and focus inwhich variations of the transfer pattern are within a predeterminedrange, and takes their central values as the optimum values of exposureenergy and focus offset.
 4. The method for exposure processing of asemiconductor device in accordance with claim 2, wherein the exposuredevice assignment step comprises: (1) a step of calculating anassignment priority order for each exposure device, based on orderconditions for the semiconductor device and on production progressinformation of a semiconductor fabrication line; (2) a step ofcalculating an assignment priority order from margins of exposure energyand focus calculated in the exposure parameter calculation step; and (3)a step of calculating an assignment priority order in a process usingweighting functions set for the semiconductor device in accordance withthe assignment priority orders of the exposure devices calculated insaid steps (1) and (2).